1. Field of the Invention
The present invention relates to a substrate processing apparatus and a gas supply method, and in particular to a substrate processing apparatus having a gas supply unit that supplies hydrogen fluoride gas into a processing chamber.
2. Description of the Related Art
In a semiconductor device manufacturing method of manufacturing semiconductor devices from silicon wafers (hereinafter referred to as “wafers”), a film formation process such as CVD (chemical vapor deposition) in which a conductive film or an insulating film is formed on a surface of a wafer, a lithography process in which a photoresist layer with a desired pattern is formed on the formed conductive film or insulating film, and an etching process in which a conductive film is formed into a gate electrode through plasma produced from a processing gas using the photoresist layer as a mask, or wiring trenches and contact holes are formed in the insulating film are repeatedly carried out in sequence.
For example, in a certain semiconductor device manufacturing method, there may be a case where a polysilicon layer formed on a wafer is etched using a hard mask formed with a predetermined pattern. In this case, a deposit film comprised of SiOBr is formed on a side of a trench formed through etching. It should be noted that SiOBr has a similar property to SiO2.
Meanwhile, the deposit film may cause defects of a semiconductor device, such as a conduction failure, and hence have to be removed. Moreover, to increase throughput, it is preferred that the deposit film and the hard mask formed on the wafer are removed at the same time.
Conventionally, as a method of removing a deposit film and a hard mask at the same time, there has been known a substrate processing method in which a chemical reaction process using hydrogen fluoride gas and a heating process are carried out on a wafer. Also, as a substrate processing apparatus that carries out the substrate processing method involving the chemical reaction process and the heating process, there has been known a substrate processing apparatus that has a chemical reaction processing device and a heating processing device connected to the chemical reaction processing device (see, for example, the specification of Japanese Patent Application No. 2006-280461).
In general, the chemical reaction processing device has a processing chamber that houses a wafer, a gas supply unit that supplies a processing gas into the processing chamber, and a mounting stage on which the wafer is mounted, wherein the gas supply unit is disposed to face the wafer mounted on the mounting stage and has a number of small-diameter gas supply holes dispersed on a surface facing the wafer. The gas supply unit supplies a processing gas into the processing chamber from an area of a higher pressure than the pressure in the processing chamber so as to function as a GDP (gas distribution plate) that discharges the processing gas uniformly toward the wafer.
In general, when gas is discharged in a stroke from a high-pressure area to a low-pressure area, there may be a case where the temperature of the gas decreases due to adiabatic expansion, causing the gas to liquefy. For this reason, considering the above temperature decrease caused by adiabatic expansion, a processing gas to be supplied into the processing chamber of the chemical reaction processing device is usually heated to a predetermined temperature in advance, and hence even when the processing gas is discharged in a stroke from a high-pressure area to a low-pressure area, the processing gas can be maintained in gaseous form.
However, when supplied at a high pressure and at a low temperature, the hydrogen fluoride gas lies in a high polymer state due to clustering of hydrogen fluoride molecules, i.e. chain combination of the hydrogen fluoride molecules. When the hydrogen fluoride gas is discharged in a stroke from a high-pressure area to a low-pressure area, the temperature of the hydrogen fluoride gas suddenly decreases due to dissociation of the clustered hydrogen fluoride molecules as well as adiabatic expansion, and hence the hydrogen fluoride gas cannot be maintained in gaseous form. Specifically, the temperature of the hydrogen fluoride gas becomes lower than a boiling point in the vicinity of openings of the gas supply holes leading into the processing chamber, and the hydrogen fluoride gas thus liquefies in the vicinity of the openings. The liquefied hydrogen fluoride is turned into deposit in the vicinity of the openings, and the deposit obstructs the discharge of hydrogen fluoride gas. As a result, hydrogen fluoride gas cannot be discharged uniformly toward a wafer, and this affects processing carried out on the wafer. Further, if the deposit is caused to fall off by the discharge of hydrogen fluoride gas, and the deposit caused to fall off becomes attached to the surface of a wafer, this may cause defects of a semiconductor device ultimately manufactured.